Method for producing a semiconductor component

ABSTRACT

Presented is a method for producing an optoelectronic component. The method includes separating a semiconductor layer based on a III-V-compound semiconductor material from a substrate by irradiation with a laser beam having a plateau-like spatial beam profile, where individual regions of the semiconductor layer are irradiated successively.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/503,042, filed on May 24, 2005, which is a U.S. national stage ofInternational Application No. PCT/DE03/00260, filed on 30 Jan. 2003.Priority is claimed to German Patent Application No. 102 03 795.7, filedJan. 31, 2002, and German Patent Application No. 102 43 757.2, filedSep. 20, 2002. The entire content of U.S. patent application Ser. No.10/503,042, German Patent Application No. 102 03 795.7, and GermanPatent Application No. 102 43 757.2 are incorporated herein byreference.

TECHNICAL FIELD

The invention relates to a method for producing a semiconductorcomponent, in which a semiconductor layer is separated from a substrateby irradiation with a laser beam.

BACKGROUND OF THE INVENTION

A method of this type is used for example in the production ofsubstrateless luminescence diodes based on GaN. Such components containa semiconductor body and a carrier part, on which the semiconductor bodyis fixed. In order to produce the semiconductor body, firstly asemiconductor layer is fabricated on a suitable substrate, subsequentlyconnected to a carrier and then stripped away from the substrate.Dividing up, for example sawing up, the carrier with the semiconductorlayer arranged thereon produces a plurality of semiconductor bodies,which are in each case fixed on the corresponding carrier part. What isessential in this case is that the substrate used for producing thesemiconductor layer is removed from the semiconductor layer and does notsimultaneously serve as a carrier or carrier part in the component.

This production method has the advantage that different materials areused for the substrate and the carrier. The respective materials canthus be adapted, largely independently of one another, to the variousrequirements for the production of the semiconductor layer, on the onehand, and the operating conditions, on the other hand. Thus, the carriercan be chosen in accordance with its mechanical, thermal and opticalproperties independently of the requirements made of the substrate forthe fabrication of the semiconductor layer.

The epitaxial production of a semiconductor layer, in particular, makesnumerous special requirements of the epitaxial substrate. By way ofexample, the lattice constants of the substrate and of the semiconductorlayer to be applied have to be adapted to one another. Furthermore, thesubstrate should withstand the epitaxy conditions, in particulartemperatures of up to in excess of 1000° C., and be suitable for theepitaxial accretion and growth of an as far as possible homogeneouslayer of the relevant semiconductor material.

By contrast, other properties of the carrier such as, by way of example,electrical and thermal conductivity and also radiation transmissivity inthe case of optoelectronic components come to the fore for the furtherprocessing of the semiconductor body and operation. Therefore, thematerials suitable for an epitaxial substrate are often only suitable toa limited extent as carrier part in the component. Finally, it isdesirable, particularly in the case of comparatively expensive epitaxialsubstrates such as silicon carbide substrates, for example, to be ableto use the substrates repeatedly.

The stripping-away of the semiconductor layer from the substrate isessential for the aforementioned production method. Said stripping-awaycan be achieved by irradiating the semiconductor-substrate interfacewith laser radiation. In this case, the laser radiation is absorbed inthe vicinity of the interface, where it effects decomposition of thesemiconductor material.

The semiconductor layer may be separated from the substrate for exampleby means of laser stripping, as described in the document U.S. Pat. No.6,559,075. In this case, the frequency-tripled radiation of a Q-switchNd:YAG laser at 355 nm is used for stripping GaN and GaInN layers from asapphire substrate. The sapphire substrate is transparent to radiationat this wavelength. The radiation energy is absorbed in a boundary layerhaving a thickness of approximately 100 nm at the junction between thesapphire substrate and the GaN semiconductor layer. At pulse energies ofabove 200 mJ/cm², temperatures of more than 850° C. are reached at theinterface. The GaN boundary layer decomposes at this temperature toliberate nitrogen, and the bond between the semiconductor layer and thesubstrate is separated.

In the case of a method of this type, there is the risk of substrateresidues adhering on the semiconductor layer on account of incompletematerial decomposition during the stripping away of the semiconductorlayer. By way of example, microscopic sapphire grains, so-called“flakes”, are often found on a GaN layer separated from a sapphiresubstrate in this way.

The diameter of these sapphire residues typically lies between 5 μm and100 μm. The sapphire residues make further processing of thesemiconductor layer more difficult and require a comparatively higheffort to remove them on account of the high mechanical and chemicalresistance of sapphire. This may have the effect that only parts of thestripped-away semiconductor layer can continue to be used or the entirelayer even becomes unusable.

Generally, a mechanical stabilization of the semiconductor layer to bestripped away is necessary since the layer thickness is so small thatotherwise there is the risk of damage, in particular a break or crack inthe layer. By way of example, a connection of the semiconductor layer,which may also already be partly processed, to the carrier by means of amaterial joint is suitable for the purpose of mechanical stabilization.Such a connection should be thermostable at least to an extent such thatit withstands without damage the temperatures that occur duringsubsequent fabrication steps. Furthermore, said connection should alsoremain stable in the event of alternating temperature loads which mayoccur, in particular, during operation of the component.

Adhesives are often used for fixing the semiconductor layer on thecarrier. In the case of relatively high electrical powers, problems mayresult in this case on account of the limited thermal and electricalconductivity of adhesives. The limited thermal endurance of suchadhesive connections additionally limits the permissible temperaturerange of a corresponding component and consequently the maximum possiblepower loss.

SUMMARY OF THE INVENTION

In one aspect, the invention involves a method for producing anoptoelectronic component. The method includes separating a semiconductorlayer based on a III-V-compound semiconductor material from a substrateby irradiation with a laser beam having a plateau-like spatial beamprofile, where a plurality of individual regions of the semiconductorlayer are irradiated successively.

In some embodiments, the laser beam is generated by an excimer laser.The excimer laser contains a noble gas-halogen compound as laser-activemedium, such as XeF, XeBr, XeCl, KrCl, or KrF. The laser beam has arectangular or trapezoidal spatial beam profile. The laser beam isgenerated by a laser in pulsed operation. The wavelength of the laserbeam is between 200 nm and 400 nm. The laser beam is focused onto thesemiconductor layer in such a way that, within the irradiated region,the energy density generated by the laser beam is between 100 mJ/cm² and1000 mJ/cm².

In another embodiment, the individual regions are arranged inarea-filling fashion such that a spatially approximately constantintensity distribution results, in a manner integrated with respect totime, for a predominant part of the irradiated semiconductor layer.

In still another embodiment, the laser beam has, at the location of thesemiconductor layer, a beam area with a longitudinal dimension (a) and atransverse dimension (b), the longitudinal dimension (a) is greater thanthe transverse dimension (b), and the semiconductor layer is movedrelative to the laser beam during the irradiation along the direction ofthe transverse dimension (b).

In still another embodiment, the substrate is at least partlytransmissive to the laser beam and the semiconductor layer is irradiatedthrough the substrate.

In other embodiments, prior to separation from the substrate, thesemiconductor layer is applied onto a carrier on a side remote from thesubstrate.

In one embodiment, the thermal expansion coefficient of the carriera_(HL) is chosen in a manner coordinated with at least one of the beamprofile and the pulse length of the laser beam pulses and with thethermal expansion coefficient of the semiconductor layer a_(HL) and thethermal expansion coefficient a_(HL) of the substrate, in order toreduce strains between the substrate, the semiconductor layer, and thecarrier during production.

In another embodiment, the thermal expansion coefficient of the carriera_(HL) is chosen to be nearer to the thermal expansion coefficient ofthe semiconductor layer a_(HL) than to the thermal expansion coefficientas of the substrate.

In still another embodiment, the thermal expansion coefficient of thecarrier a_(HL) differs from the thermal expansion coefficient a_(HL) ofthe substrate by 45% or less.

In another embodiment, the thermal expansion coefficient of the carrierdiffers from the thermal expansion coefficient a_(HL) of thesemiconductor layer by 35% or less.

In still another embodiment, the carrier has a thermal expansioncoefficient of approximately 4.3*10⁻⁶K⁻¹ and approximately 5.9*10⁻⁶K⁻¹.

In other embodiments, the carrier includes at least one of galliumarsenide, silicon, copper, iron, nickel, cobalt, molybdenum, tungsten,and germanium.

In another embodiment, a large pulse length of the laser beam pulses ischosen for the separation of the semiconductor layer from the substrate.

In still another embodiment, the thermal expansion coefficient of thecarrier a_(HL) differs from the thermal expansion coefficient a_(HL) ofthe semiconductor layer by 35% or more, and in which a small pulselength of the laser beam pulses is chosen for the separation of thesemiconductor layer from the substrate.

In yet another embodiment, the semiconductor layer is soldered onto thecarrier by means of a solder containing at least one of gold, tin,palladium and indium.

In another embodiment, before the semiconductor layer is connected tothe carrier, a metallization is applied to the side of the semiconductorlayer which is remote from the substrate. The metallization includes atleast one of gold and platinum.

In one embodiment, the semiconductor layer includes a plurality ofindividual layers. The III-V compound semiconductor material is anitride compound semiconductor material.

In another embodiment, the semiconductor layer or at least one of theindividual layers comprises In_(x)Al_(y)Ga_(1-x-y)N where 0≦x≦1, 0≦y≦1and x+y≦1, such as GaN, A1GaN, InGaN, AlInGaN, AlN or InN. The substratecontains at least one of silicon, silicon carbide, aluminium oxide,sapphire.

In still another embodiment, the semiconductor layer is epitaxiallygrown on the substrate. The semiconductor layer has a thickness which isless than or equal to 50 μm. The semiconductor component is a lightemitting diode.

In yet another embodiment, an interface region between semiconductorlayer and substrate is irradiated in such a way that the radiationenergy is absorbed at said interface region, said absorption ofradiation energy leading to a material decomposition within thesemiconductor layer.

In another embodiment, the laser beam is focused onto the semiconductorlayer in such a way that, within the irradiated region, the energydensity generated by the laser beam is between 150 mJ/cm² and 800mJ/cm².

In still another embodiment, the thermal expansion coefficient of thecarrier a_(HL) differs from the thermal expansion coefficient a_(HL) ofthe substrate by 40% or less.

In another embodiment, the thermal expansion coefficient of the carriera_(HL) differs from the thermal expansion coefficient a_(HL) of thesemiconductor layer by 25% or less.

In yet another embodiment, the carrier has a thermal expansioncoefficient of approximately 4.6×10⁻⁶K⁻¹ and approximately 5.3*10⁻⁶K⁻¹.

In other embodiments, prior to separation from the substrate, thesemiconductor layer is soldered onto a carrier on a side remote from thesubstrate.

In another embodiment, a pulse length of greater than 15 ns of the laserbeam pulses is chosen for the separation of the semiconductor layer fromthe substrate.

In still another embodiment, the thermal expansion coefficient of thecarrier a_(HL) differs from the thermal expansion coefficient a_(HL) ofthe semiconductor layer by 35% or more, and in which a pulse length ofless than approximately 15 ns of the laser beam pulses is chosen for theseparation of the semiconductor layer from the substrate.

In a particular embodiment, the laser beam can have a rectangular ortrapezoidal beam profile. This beam profile significantly reduces thenumber of substrate residues on the semiconductor layer in comparisonwith a conventional separation method.

A plateaulike beam profile is to be understood to be a transversalintensity distribution of the laser beam which has a central region withan essentially constant intensity distribution adjoined in each case bya flank with falling intensity. Preferably, the relative fluctuation ofthe beam intensity in the central region is less than 5 percent.

In order to further improve the beam profile, a beam homogenizer may bearranged downstream of the laser. Furthermore, it is expedient to use asuitable optical arrangement, for example a lens system which maycomprise correction lenses, attenuators, mirrors, mask structures and/orprojection lenses, for imaging the laser beam onto the semiconductorlayer. In this way, it is possible to set the energy density requiredfor material decomposition without impairing the advantageous beamprofile.

By contrast, the lasers used in conventional laser separation methodsgenerally have a Gaussian beam profile. This leads to a spatiallycomparatively greatly varying, inhomogeneous field distribution on thesemiconductor-substrate interface and consequently to varying degrees ofmaterial decomposition. During the subsequent stripping-away of thesemiconductor layer, there is the risk of substrate residues adhering onthe semiconductor layer at locations of weak or incomplete materialdecomposition.

Preferably, in the case of the invention, the laser beam is generated byan excimer laser. Excimer lasers generally have a plateaulike, oftentrapezoidal or rectangular, beam profile. Furthermore, particularly inthe case of excimer lasers with a noble gas-halogen compound as lasermedium, the emission wavelength lies in the ultraviolet spectral range,which is particularly suitable for stripping away nitride compoundsemiconductors. Moreover, the pulse peak power in the case of excimerlasers, which typically lies between 1 kW and 100 MW, is so high thateven in the event of mask imagings of the laser beam and after passagethrough a plurality of lenses, the energy density suffices for materialdecomposition.

In order to achieve the beam intensity required for the materialdecomposition, a pulsed operation is expedient for the laser. Incomparison with a laser in continuous wave operation, this also reducesthe risk of overheating of the semiconductor layer that is to bestripped away. In the case of a pulsed laser, the transporting-away ofthe heat arising as a result of the laser irradiation can be setoptimally through a suitable choice of pulse duration and pulse spacing.

In the case of semiconductor layers with a relatively large lateralextent, it is advantageous for individual regions of the semiconductorlayer that are arranged next to one another to be irradiatedsuccessively, in order to avoid an excessively large expansion of thebeam area. Since, for a given beam power or energy of the laser pulse,the intensity decreases as the beam area increases, it is possible, inthe event of excessively great beam expansion, for the decompositionthreshold, i.e. the energy density required for the materialdecomposition, to be undershot and complete stripping-away of thesemiconductor layer to be impaired.

In this case, it is particularly advantageous to guide the laser beamand/or the substrate with the semiconductor layer situated thereon suchthat the irradiated individual regions produce an area-filling overallarrangement. An approximately constant spatial intensity distributionfor the predominant part of the irradiated area corresponds to this in amanner integrated with respect to time, i.e. over the irradiation timeperiod. On account of this approximately constant intensitydistribution, the stripped-away semiconductor layer has anadvantageously small number of substrate residues or is even free ofresidues. A plateaulike, in particular rectangular, spatial beam profileis particularly advantageous for the abovementioned area-filling overallarrangement of the irradiated individual regions.

In a preferred development of the invention, the laser beam has, at thelocation of the semiconductor layer or the semiconductor-substrateinterface, a beam area with a longitudinal dimension and a transversedimension, the longitudinal dimension being significantly greater thanthe transverse dimension. Preferably, the longitudinal dimension exceedsthe transverse dimension by a factor of 5 to 10, thus producing a linearor striplike beam area.

The semiconductor layer is moved during irradiation in a paralleldirection with respect to the transverse dimension, so that, duringirradiation, the linear or striplike beam area sweeps over the entiresemiconductor layer to be stripped away. In this case, too, anadvantageously constant intensity distribution of the irradiatedsemiconductor layer results in a manner integrated over the irradiationtime period, a further advantage consisting in the fact that a simplelinear movement of the semiconductor layer relative to the laser beamsuffices. It goes without saying that this involves a relative movementbetween semiconductor layer and laser beam which can be realized both bymeans of a movement of the semiconductor layer with a stationary laserbeam and by means of a corresponding guidance of the laser beam with astationary semiconductor layer.

In the case of the invention, it is advantageous to irradiate the directinterface region between semiconductor layer and substrate with thelaser radiation, so that the radiation energy is absorbed near theinterface and leads to a material decomposition there. This may beachieved by virtue of the fact that the substrate is transmissive to thelaser radiation and the semiconductor layer is irradiated through thesubstrate. In the case of this arrangement, the absorption of the laserradiation is generally significantly greater in the semiconductor layerthan in the substrate, so that the laser beam penetrates through thesubstrate virtually without any losses and is absorbed on account of thehigh absorption near the interface in the semiconductor layer.

It should be noted that the radiation absorption need not necessarily beeffected at the location of material decomposition. The materialdecomposition may also be effected by the radiation firstly beingabsorbed at a different location and then the absorbed radiation energybeing transported to the location of material decomposition. Ifappropriate, the radiation could also be absorbed in the substrate andthe radiation energy could subsequently be transported to thesemiconductor layer.

A further aspect of the invention is directed to a method for producinga semiconductor component, in which a semiconductor layer is separatedfrom a substrate by means of a laser beam. Prior to separation, thesemiconductor layer is applied, preferably soldered, onto a carrier bythe side remote from the substrate. A soldered connection isdistinguished by a high thermal and electrical conductivity incomparison with conventional adhesive connections.

The separation itself is preferably effected according to one of themethods already described. It goes without saying that although asoldered connection is advantageous in the case of the separationmethods described previously, an adhesive-bonding connection betweencarrier and semiconductor layer also lies within the scope of theinvention.

The solder used is preferably a gold-containing solder, for example agold-tin solder. Gold-tin solders having a high proportion of gold, forexample between 65% by weight and 85% by weight, are particularlypreferred in this case.

The melting point of such a solder is typically 278° C. and is thusgreater than the temperature which usually arises during the solderingof an electrical component. Thus, by way of example, the solderingtemperature in the course of soldering onto a printed circuit board isgenerally less than 260° C. This prevents the semiconductor body frombeing stripped away from the carrier part when the component is solderedin.

Furthermore, an example of a suitable solder is a palladium-indiumsolder, the constituents of which are intermixed at a comparatively lowinitial temperature of approximately 200° C., and which has anadvantageously high melting point of in excess of 660° C. afterintermixing.

Such a connection may be produced for example by applying an indiumlayer on the semiconductor layer and a palladium layer on the carrierand then joining together the carrier and the semiconductor layer underincreased pressure at a temperature of approximately 200° C. or more.

It goes without saying that it is also possible for the palladium layerto be applied on the semiconductor layer and the indium layer to beapplied on the carrier. Moreover, it is advantageous to provide furtherlayers between the semiconductor layer and the metal layer, said furtherlayers ensuring for example protection of the semiconductor layer orgood adhesion. A layer sequence with a titanium layer on thesemiconductor surface, then a palladium layer and an indium layerthereon is particularly advantageous in conjunction with a palladiumlayer on the carrier.

With regard to a low contact resistance and advantageous solderingproperties, it is expedient to provide the semiconductor layer with acontact metallization on the side facing the carrier, prior to solderingonto the carrier. A platinum-gold metallization, for example, issuitable for this purpose.

In a further aspect of the invention, it is provided that the thermalexpansion coefficient of the carrier a_(T) is chosen in a mannercoordinated with the thermal expansion coefficient of the semiconductorlayer a_(HL) and/or the thermal expansion coefficient of the substratea_(S) and also, if appropriate, the beam profile and the pulse length ofthe laser beam pulses. Generally, a coordination of the thermalexpansion coefficients is to be understood to mean that their differenceis so small that, in the temperature range that occurs during productionor is provided in operation, no damage is produced at the semiconductorlayer and the carrier. In particular, this makes it possible tosignificantly reduce strains between substrate, semiconductor layer andcarrier during production. The risk of cracking in the carrier and inthe semiconductor layer is thus greatly decreased.

It has been observed in this respect in the context of the inventionthat the spot profiles (intensity profiles) of the laser pulses used forstripping away the semiconductor layers are often revealed after thelaser bombardment on the semiconductor surface. In the case where GaNsemiconductor layers are stripped away, metallic gallium remains on thesurface, for instance, after the dissociation of the GaN. The inventors'examinations furthermore revealed that cracks arise in the GaN materialat the edges of the laser spots, which cracks, during further processingof the material, lead to the local flaking-away of the semiconductorlayer from the underlying carrier.

It has now been found that primarily thermal effects are responsible forthis. In order, in the case of a GaN semiconductor layer, for instance,to achieve a dissociation of the GaN, it is necessary locally to achievetemperatures of approximately 800° C. to 1000° C. in the semiconductorlayer. If the energy density decreases greatly at the edge of the laserspot, then the temperatures required for stripping away can be reachedwithin the laser spot, while the semiconductor material remainscomparatively cold in the direct vicinity of the laser spot.

Although the temperatures reached at the GaN surface decreasesignificantly over the layer thickness of the semiconductor layer,temperatures of up to 400° C. are still reached at the carrier side ofthe semiconductor layer in the region of the laser spot. Consequently,tensile strains arise on account of the locally different temperaturesin the laser spot and outside the spot both in the semiconductor layerand in the carrier on account of the generally different thermalexpansion coefficients of the semiconductor material and the carriermaterial, and may lead to the observed formation of cracks in thesemiconductor material at the laser spot edges.

During the further processing of such semiconductor layers provided withcracks, the problem arises, for example, that acid can creep along thecracks under the semiconductor layer and, for instance, destroys abonding metallization there.

In the case of the invention, use is preferably made of special carriermaterials that are adapted in terms of their thermal properties. In thiscase, two process steps, in particular, namely the bonding process andthe laser irradiation are taken into account for the choice of thethermal expansion coefficient of the carrier a_(T).

During the bonding process, the substrate with the semiconductor layerepitaxially coated thereon, together with the carrier, is heated inwhole-area fashion to a temperature of typically approximately 400° C.and subsequently cooled down again gradually to room temperature. Inthis step, the strain balance of the layer assemblysubstrate/semiconductor layer/carrier is essentially determined by thesubstrate and the carrier. If the thermal expansion coefficients ofsubstrate and carrier, a_(S) and a_(T), deviate too greatly from oneanother, then the layer assembly may buckle as it cools down. Cracks mayalso form in the carrier, so that the resulting chip no longer hassufficient stability.

This problem is illustrated by way of example in FIG. 7. In the case ofthe layer assembly 20 illustrated diagrammatically there, a GaNsemiconductor layer 21 is grown on a sapphire substrate 22. That side ofthe semiconductor layer 21 which is remote from the substrate 22 isprovided with a contact metallization 23. A bonding wafer is soldered ascarrier 24 on the contact metallization 23 at a temperature ofapproximately 400° C.

If the thermal expansion coefficient a_(T) of the carrier issignificantly less than the thermal expansion coefficient a_(S) of thesapphire substrate, then cracks 25 may form in the carrier 24 duringthis bonding step.

During the laser irradiation, the semiconductor material is locallyheated within the laser spot to a temperature above the decompositiontemperature of the semiconductor material, while the substrate materialremains cold on account of its substantially lower absorption of thelaser radiation. Since the laser irradiation eliminates the bond betweenthe semiconductor material and the substrate by dissociation, thedifference between the thermal expansion coefficients of semiconductorlayer and carrier, a_(HL) and a_(T), determines the strain balance inthe layer assembly. In the event of a large difference between a_(HL)and a_(T), tensile strains may arise, which may lead to cracking in thesemiconductor material at the locations of the spot edges.

FIG. 8 elucidates the problem area once again for stripping away a GaNlayer 21 from a sapphire substrate 22. When the layer assembly 20 isirradiated with short laser pulses 26 of an excimer laser, the laserradiation is absorbed in a region 27 of the GaN layer 21 near theboundary and generates temperatures of 800° C. to 1000° C. there.Temperatures of up to approximately 400° C. are still reached on thatside of the semiconductor layer 21 which is remote from the substrateand in the adjoining region 28. The GaN layer 21 and the contactmetallization 23 remain comparatively cold outside the laser spot. Thetemperature in the regions 29 and 30 which laterally directly adjoin thelaser spot is typically significantly less than 300° C. In the event ofgreatly different thermal expansion coefficients between the GaN layer21 and the material of the carrier 24 or the bonding wafer, cracks 31may thus arise in the epitaxial GaN layer 21.

In order to avoid cracking in the carrier and in the epitaxialsemiconductor layer, it is therefore necessary to choose a carriermaterial whose thermal expansion coefficient a_(T) does not differ toogreatly either from the thermal expansion coefficient of the substratea_(S) or from the thermal expansion coefficient of the semiconductorlayer a_(HL). The radiation profile and the pulse length of the laserradiation also influence the choice of a suitable thermal expansioncoefficient a_(T), as will be explained in even more detail furtherbelow.

A preferred refinement of the method according to the invention providesfor the thermal expansion coefficient of the carrier a_(T) to be chosento be nearer to the thermal expansion coefficient of the semiconductorlayer a_(HL) than to the thermal expansion coefficient a_(S) of thesubstrate. Such a choice enables the formation of cracks in thesemiconductor layer to be effectively reduced or wholly avoided.

In this case it is expedient if the thermal expansion coefficient of thecarrier a_(T) differs from the thermal expansion coefficient a_(S) ofthe substrate by 45% or less, preferably by 40% or less.

In particular, for a sapphire substrate having a thermal expansioncoefficient of

a(Al₂O₃)=7.5*10⁻⁶K⁻¹

a carrier material is preferred whose thermal expansion coefficienta_(T), although it lies below a(Al₂O₃), is nevertheless greater than4.125*10⁻⁶K⁻¹, in particular greater than 4.5*10⁻⁶K⁻¹.

With regard to the thermal properties of the semiconductor layer, it isadvantageous if the thermal expansion coefficient of the carrier a_(T)differs from the thermal expansion coefficient a_(HL) of thesemiconductor layer by 35% or less, preferably by 25% or less. Inparticular when stripping away a nitride compound semiconductor layersuch as, for example, a GaN-based semiconductor layer having a thermalexpansion coefficient of

a(GaN)=4.3*10⁻⁶K⁻¹,

a carrier material is preferred whose thermal expansion coefficienta_(T), although it is greater than a(GaN), is nonetheless less than5.8*10⁻⁶K⁻¹, in particular less than 5.6*10⁻⁶K⁻¹.

Consequently, a carrier having a thermal expansion coefficient ofbetween 4.125*10⁻⁶K⁻¹ and 5.8*10⁻⁶K⁻¹, in particular between 4.5*10⁻⁶K⁻¹and 5.6*10⁻⁶K⁻¹, is particularly well suited to the stripping-away of anitride compound semiconductor layer, for instance a GaN or GaInN layer,from a sapphire substrate.

Given such a choice of thermal expansion coefficient a_(T) a large pulselength of the laser beam pulses, in particular a pulse length of greaterthan 15 ns, can be chosen for the separation of the semiconductor layerfrom the substrate without resulting in cracking in the semiconductorlayer.

In a particularly preferred refinement of the invention, the carriercontains molybdenum. The thermal expansion coefficient of molybdenum

a(Mo)=5.21*10⁻⁶K⁻¹

lies significantly nearer to a(GaN) than, for example, the thermalexpansion coefficient of GaAs where a(GaAs)=6.4*10⁻⁶K⁻¹. Theabovementioned problem area of cracking during the laser bombardment issignificantly reduced in the case of the layer assembly molybdenumbonding wafer/GaN semiconductor layer/sapphire substrate. Moreover,molybdenum is stable enough such that cracks do not arise during bondingor during cooling from the bonding temperature to room temperature.

In a further preferred refinement of the method according to theinvention, the carrier contains an iron-nickel-cobalt alloy, whichlikewise has a favorable thermal expansion coefficient of

a(Fe—Ni—Co)=5.1*10⁻⁶K⁻¹

Tungsten having a thermal expansion coefficient of

a(Wo)=4.7*10⁻⁶K⁻¹

has also been found to be an advantageous material for the carrier. Itis generally shown that the metallic carrier materials are scarcelysensitive to cracking on account of their toughness during the bondingprocess and during cooling to room temperature.

It is also possible within the scope of the invention, in the selectionof the thermal expansion coefficient of the carrier, to permit a greatertolerance with regard to the thermal expansion coefficient of thesemiconductor layer if shorter laser pulses are used. Thus, according tothe invention, the thermal expansion coefficient of the carrier a_(T)may differ from the thermal expansion coefficient a_(HL) of thesemiconductor layer by 35% or more if a small pulse length of the laserbeam pulses, in particular a pulse length of less than approximately 15ns, is chosen for the separation of the semiconductor layer from thesubstrate. This permits, in particular, the use of a GaAs bonding waferwhere a(GaAs)=6.4*10⁻⁶K⁻¹ with short pulse duration.

A preferred further development of the method according to the inventionprovides for the abovementioned carriers having an adapted thermalexpansion coefficient to be used in the stripping method described abovewith a laser beam having a plateaulike beam profile. This also includes,in particular, the advantageous refinements described, such as the useof an excimer laser, for example with XeF, XeBr, XeCl, KrCl or KrF aslaser-active medium, the formation of a rectangular or trapezoidalspatial radiation profile, the selection of an emission wavelength ofbetween 200 nm and 400 nm, the downstream arrangement of suitableoptical arrangements and/or a beam homogenizer or the subsequentirradiation of the substrate in a plurality of individual regions of thesemiconductor layer.

Furthermore, as already described, prior to stripping, the semiconductorlayer may be soldered onto the carrier by means of a gold-tin solder,preferably with a high proportion of gold of 65% by weight to 85% byweight, or by means of a palladium-indium solder, it optionally beingpossible for a metallization containing gold and/or platinum, forexample, also to be applied to that side of the semiconductor layerwhich is remote from the substrate.

It has been found as a further advantage of the method according to theinvention that the use of thermally adapted carriers also solves theproblem of inadequate adhesion between semiconductor layer and carrier,which has been observed in the past for example in the case of epitaxialGaN layers in conjunction with GaAs bonding wafers as the carrier. Thecontrol of the strain balance in the entire layer assembly according tothe present invention also includes the bonding metallization and thusprovides an effective remedy with regard to the aforementioned problemarea of adhesion.

The invention is suitable in particular for semiconductor layerscontaining a nitride compound semiconductor. Nitride compoundsemiconductors are for example nitride compounds of elements of thethird and/or fifth main group of the Periodic Table, such as GaN, AlGaN,InGaN, AlInGaN, InN or AlN. In this case, the semiconductor layer mayalso comprise a plurality of individual layers of different nitridecompound semiconductors. Thus, the semiconductor layer may have forexample a conventional pn junction, a double heterostructure, a singlequantum well structure (SQW structure) or a multiple quantum wellstructure (MQW structure). Such structures are known to the personskilled in the art and are therefore not explained in any greater detailat this point. Such structures are preferably used in optoelectroniccomponents such as light emission diodes such as light-emitting diodes(LEDs) or laser diodes.

It should be noted that generally in the context of the invention, inparticular for nitride compound semiconductors, a carrier is suitablewhich contains gallium arsenide, germanium, molybdenum, silicon or analloy, for example based on iron, nickel and/or cobalt. Carriers basedon the abovementioned advantageous materials molybdenum, tungsten or aniron-nickel-cobalt alloy are preferably used.

Examples of a suitable substrate for the epitaxial fabrication ofnitride compound semiconductor layers are silicon, silicon carbide oraluminum oxide or sapphire substrates, sapphire substratesadvantageously being transmissive to the laser radiation used for theseparation of the semiconductor layer, in particular in the ultravioletspectral range. This enables irradiation of the semiconductor layerthrough the substrate when stripping away the semiconductor layer.

The method according to the invention may advantageously be employed inthe case of thin-film chips typically having a semiconductor layer witha thickness of less than approximately 50 μm. The thin-film chip may befor example an optoelectronic chip, in particular a radiation-generatingchip such as a luminescence diode chip, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures, identical or identically acting elements are providedwith the same reference symbol.

FIGS. 1A to 1E show a diagrammatic illustration of a first exemplaryembodiment of a method according to the invention on the basis of fiveintermediate steps,

FIGS. 2A and 2B respectively show a diagrammatic illustration of twovariants of a second exemplary embodiment of a method according to theinvention,

FIGS. 3B and 3 b show a diagrammatic illustration of a beam profile ofthe laser beam in the case of the method shown in FIG. 2A,

FIG. 4 shows a diagrammatic illustration of the resulting intensitydistribution in the case of the method illustrated in FIG. 2A,

FIG. 5 shows a diagrammatic illustration of a third exemplary embodimentof a method according to the invention,

FIGS. 6A to 6C show a diagrammatic illustration of a production methodwith the use of Gaussian intensity distributions,

FIG. 7 shows a diagrammatic illustration for elucidating the arising ofcracks in the carrier, and

FIG. 8 shows a diagrammatic illustration for elucidating the arising ofcracks in the semiconductor layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the first step of the method illustrated in FIG. 1, FIG. 1A, asemiconductor layer 2 is applied to a substrate 1. This may be a nitridecompound semiconductor layer, for example an InGaN layer, which is grownepitaxially onto a sapphire substrate. More widely, the semiconductorlayer 2 may also comprise a plurality of individual layers which maycontain for example GaN, AlN, AlGaN, InGaN, InN or InAlGaN and be grownsuccessively onto the substrate 1.

In the next step, FIG. 1B, the semiconductor layer 2 is provided with acontact metallization 3 on the side remote from the substrate. Thecontact metallization 3 results in a low contact resistance between thesemiconductor layer 2 and an electrical connection, for example aconnecting wire, that is to be fitted in a later method step. Moreover,the contact metallization 3 improves the soldering properties of thesemiconductor layer 2.

The contact metallization 3 may be vapor-deposited or sputtered on forexample in the form of a thin gold- and/or platinum-containing layer.

Afterward, a carrier 4 is soldered onto the contact metallization 3,FIG. 1C. The solder 5 used is preferably a gold-containing solder, forexample a gold-tin solder with a gold proportion of between 65% byweight and 85% by weight, preferably 75% by weight. Such a solderingconnection is distinguished by a high thermal conductivity and a highstability under alternating temperature loads.

The soldering connection may be formed at a joining temperature of 375°C., a comparatively low joining pressure of less than 1.0 bar beingnecessary. This low joining pressure makes it possible, even in the caseof very thin semiconductor layers, to effect a connection to the carrier4 without mechanical damage to the semiconductor layer 2.

The carrier 4 used may be a GaAs wafer, for example, which has a similarthermal expansion coefficient to that of sapphire.

A carrier 4 in the form of a bonding wafer made of molybdenum ispreferably provided. The thermal expansion coefficients of the bondingwafer a(Mo)=5.21*10⁻⁶K⁻¹ and of the sapphire substratea(Al₂O₃)=7.5*10⁻⁶K⁻¹ are relatively close together, so that thermallyinduced strains in the semiconductor layer 2 are advantageously keptlow. Furthermore, molybdenum is sufficiently tough, so that cracks donot arise in the molybdenum bonding wafer during bonding and duringcooling from the bonding temperature to room temperature.

Instead of a GaAs wafer, a Ge wafer may also be used in the case of theinvention. The thermal expansion coefficient of germanium is similar tothat of GaAs, so that differences scarcely result in this regard.However, a Ge wafer has the advantage over a GaAs wafer that it can besawn more easily, in which case, in particular, no arsenic-containingtoxic sawing waste is obtained. Furthermore, Ge wafers are mechanicallystabler. Thus, a sufficient stability is already achieved with a 200 μmthick Ge wafer for example, whereas the thickness of a correspondingGaAs wafer is greater than 600 μm. It is advantageous that it is alsonot necessary in this case for the Ge wafer to be thinned by grinding ina further method step. Finally, Ge wafers are generally significantlymore cost-effective than GaAs wafers.

Preferably, a gold-containing solder or gold itself is used as solder inconjunction with a Ge wafer. This achieves a particularly fixedconnection to the semiconductor layer. Use is made particularlypreferably of a gold-vapor-deposited Ge wafer, which may optionally beprovided with an AuSb surface layer.

In the subsequent step, FIG. 1D, the semiconductor layer 2 is irradiatedthrough the substrate 1 with a laser beam 6 having a plateaulike beamprofile 7. The radiation energy is predominantly absorbed in thesemiconductor layer 2 and brings about a material decomposition at theinterface between the semiconductor layer 2 and the substrate 1, so thatthe substrate 1 can subsequently be lifted off.

What is essential in the case of the invention is that the beam profileand the coupled-in beam power are dimensioned such that a hightemperature that suffices for material decomposition arises locally atthe interface between the substrate 1 and the semiconductor layer 2,which temperature falls over the layer thickness of the semiconductorlayer to an extent such that the connection 5 between the carrier 4 andthe semiconductor layer is not impaired, for example by melting.

The strong mechanical loads that occur on account of the materialdecomposition are advantageously taken up by the solder layer, so thateven semiconductor layers having a thickness of a few micrometers can bestripped nondestructively from the substrate.

The transverse beam profile 7 of the laser beam 6 is likewiseillustrated in FIG. 1D. The beam intensity along the line A-A isplotted. The beam profile 7 has a central region 17, in which theintensity is essentially constant. Said central region 17 is adjoinedlaterally by flank regions 18, in which the intensity falls steeply.Depending on the type of fall, the beam profile is like a trapezoid(linear fall) or a rectangle in the case of a very steep fall.

A XeF excimer laser is particularly suitable as the radiation source. Onaccount of the high gain and the typical resonator geometry of excimerlasers, the spatial beam profile is plateaulike and thereforeparticularly suitable for the invention. Furthermore, the high pulsepeak intensity of excimer lasers in a range of 1 kW to 100 MW and alsothe emission wavelength in the ultraviolet spectral range areadvantageous in the case of the invention.

The laser radiation is focused by means of a suitable opticalarrangement through the substrate onto the semiconductor layer 2, whereit has a typical beam area of approximately 1 mm×2 mm or more. Theintensity distribution within the beam area is largely homogeneous, anenergy density of between 200 mJ/cm² and 800 mJ/cm² being achieved. Thisenergy density in conjunction with a homogeneous intensity distributionenables the semiconductor layer to be separated from the substratewithout any residues.

This has been demonstrated experimentally by way of example using anInGaN layer on a sapphire substrate. Specifically, the InGaNsemiconductor layer was irradiated with a pulsed laser beam from a XeFexcimer laser having a wavelength of 351 nm and a pulse duration of 25ns. While the sapphire substrate is transparent to radiation having thiswavelength, it is absorbed to a great extent in the InGaN semiconductorlayer. A thin boundary layer at the junction with the substrate isheated by the energy input to temperatures of 800° C. to 1000° C. Atthis temperature, the semiconductor material decomposes at the laserspot to liberate nitrogen and the bond between the semiconductor layer14 and the substrate 12 separates.

As an alternative, a comparable separation without any residues can becarried out using a KrF excimer laser. At approximately 248 nm, theemission wavelength lies further in the ultraviolet spectral range. Inthis case, even with larger beam cross sections having a dimensioning of30 mm×10 mm, the energy density, which correspondingly lies between 150mJ/cm² and 600 mJ/cm², preferably between 150 mJ/cm² and 450 mJ/cm²,suffices for separating the semiconductor layer from the substratewithout any residues. Furthermore, XeBr, XeCl, and KrCl excimer lasershaving an emission wavelength of approximately 282 nm, 308 nm and 222nm, respectively, have proved to be suitable for the invention.

After irradiation with the laser beam, the substrate 1 can be liftedoff, FIG. 1E, in which case the semiconductor layer 2 remains on thecarrier 4 largely without any substrate residues and can be processedfurther.

FIG. 2A shows a second exemplary embodiment of a method according to theinvention. In contrast to the method illustrated in FIG. 1, in this caseindividual regions 8 of the semiconductor layer 2 are successivelyexposed to the laser beam. The approximately rectangular individualregions 8 are arranged in area-filling and slightly overlapping fashion.In this case, the overlap serves to compensate for the drop in intensityin the edge regions 18 of the beam profile 7. The individual regions arefurthermore arranged in matrix-like fashion, an offset of the matrixrows with respect to one another being advantageous with regard to anintensity distribution that is as homogeneous as possible. Analternative arrangement of the individual regions 8 is illustrateddiagrammatically in FIG. 2B.

The beam profile of the laser beam within the individual region 8 isillustrated in FIGS. 3B and 3 b. In FIG. 3B, the intensity is plottedalong the X axis of the coordinate system 9 of axes depicted in FIGS. 2Aand 2B; FIG. 3 b shows the corresponding intensity profile along the Yaxis. Both profiles are plateaulike and have a central region 17 a, 17 badjoined by flanks 18 a, 18 b with a steep fall in intensity.

The intensity distribution resulting from this in the case of theindividual irradiation of the semiconductor layer as shown in FIG. 2A isillustrated in FIG. 4. The intensity along the line B-B integrated overthe entire irradiation time is plotted. The result is a largelyhomogeneous, virtually constant intensity profile over the entire areaof the semiconductor layer 2, which enables the semiconductor layer 2 tobe separated from the substrate 1 in a manner free of residues.

By contrast, FIG. 6A illustrates a corresponding method according to theprior art with regard to the beam profile. The laser used in this case,for example a frequency-tripled Nd:YAG laser, has an approximatelycircular beam area with a Gaussian beam profile 15.

A gridlike arrangement—corresponding to FIG. 2A or 2B—of successivelyirradiated regions 14 of a semiconductor layer is shown in FIG. 6A.

The associated beam profile 15, i.e. the intensity profile along the Xaxis and the Y axis of the coordinate system 9 of axes, is illustratedin FIG. 6B. On account of a rotationally symmetrical intensitydistribution, which also results in the circular beam area, theintensity profile along the two axes is approximately identical. Theintensity profile corresponds to a Gaussian curve with maximum intensityat the origin of the coordinate system 9 of axes.

In order to attain the decomposition threshold with such a laser beam,it is generally necessary to focus the beam. In this case, thedecomposition threshold is exceeded in the beam center, while the energydensity is too low for a material decomposition in the edge regions. Anapproximately constant intensity distribution, as illustrated in FIG. 4,cannot be achieved in the case of a gridlike irradiation of asemiconductor layer in accordance with FIG. 6A. The intensity variationover the entire beam profile and in particular the pronounced intensitymaximum in the beam center leads to numerous intensity maxima and minimaon the semiconductor layer.

An exemplary profile 13 of the intensity along the line C-C—shown inFIG. 6A—integrated over the entire irradiation time is illustrated inFIG. 6C. The variation of the intensity profile 13 leads to a nonuniformmaterial decomposition, in which case the decomposition threshold may beundershot in particular in the minima of the intensity distribution.

The semiconductor material is preserved at the locations at which theenergy density necessary for the material decomposition is not attained.On account of the material decomposition in the vicinity of theselocations, if appropriate with evolution of gas such as nitrogen, forexample, in the case of nitride compound semiconductors, a high pressuremay arise locally and wrench particles out of the substrate. Theseparticles may adhere to the locations where the semiconductor materialhas not decomposed, so that ultimately substrate residues remain on thestripped semiconductor layer.

In order to prevent that, the beam intensity could be increased furtherin the case of conventional methods. However, there would then be therisk of damage to the semiconductor layer due to overheating at thelocations of the intensity maxima.

FIG. 5 illustrates a third exemplary embodiment of a method according tothe invention. In contrast to the method shown in FIGS. 1 and 2, thelaser beam is in this case imaged onto the semiconductor layer 2 in sucha way that a striplike beam area 19 arises. In this case, the beam area19 has a longitudinal dimension a and a transverse dimension b, thelongitudinal dimension a being significantly greater than the transversedimension b. In the case of an excimer laser 11, a corresponding beamarea may be formed for example by means of a suitable mask opticalarrangement 12. The longitudinal dimension a is preferably greater thana corresponding dimension of the semiconductor layer 2, so that thesemiconductor layer 2 is completely irradiated in this direction. Inthis case, the fall in intensity in the flank regions 18 of the beamprofile does not affect the separation method, since the flank regions18 lie outside the semiconductor layer 2.

The semiconductor layer 2 is moved during irradiation in the directionof the transverse dimension b so that the entire semiconductor layer 2is irradiated uniformly. Given a pulsed laser with a sufficiently shortpulse duration, typically in the nanoseconds range, this once againresults in a progressive irradiation of striplike individual areas onthe semiconductor layer 2, since the semiconductor layer 2 isessentially moved further between the laser pulses and the irradiationis effected instantly relative to this movement.

It goes without saying that the explanation of the invention on thebasis of the exemplary embodiments is not to be understood as arestriction of the invention thereto. Rather, individual aspects of theexemplary embodiments can be combined largely freely within the scope ofthe invention.

The scope of protection of the invention is not restricted by thedescription of the invention on the basis of the exemplary embodiments.In fact, the invention covers any new feature as well as any combinationof features, in particular including any combination of features in thepatent claims, even if this combination is not explicitly stated in thepatent claims or in the examples.

1. A method for producing an optoelectronic component, comprising:separating a semiconductor layer based on a III-V-compound semiconductormaterial from a substrate by irradiation with a laser beam having aplateau-like spatial beam profile; wherein a plurality of individualregions of the semiconductor layer are irradiated successively.
 2. Themethod as claimed in claim 1, wherein the laser beam is generated by anexcimer laser.
 3. The method as claimed in claim 2, wherein the excimerlaser comprises a noble gas-halogen compound as laser-active medium. 4.The method as claimed in claim 1, wherein the laser beam has arectangular or trapezoidal spatial beam profile.
 5. The method asclaimed in claim 1, wherein the laser beam is generated by a laser inpulsed operation.
 6. The method as claimed in claim 1, wherein thewavelength of the laser beam is between 200 nm and 400 nm.
 7. The methodas claimed in claim 1, wherein the laser beam is focused onto thesemiconductor layer in such a way that, within the irradiated region,the energy density generated by the laser beam is between 100 mJ/cm² and1000 mJ/cm².
 8. The method as claimed in claim 1, wherein the individualregions are arranged in area-filling fashion such that a spatiallyapproximately constant intensity distribution results, in a mannerintegrated with respect to time, for a predominant part of theirradiated semiconductor layer.
 9. The method as claimed in claim 1,wherein the laser beam has, at the location of the semiconductor layer,a beam area with a longitudinal dimension (a) and a transverse dimension(b), the longitudinal dimension (a) is greater than the transversedimension (b), and the semiconductor layer is moved relative to thelaser beam during the irradiation along the direction of the transversedimension (b).
 10. The method as claimed in claim 1, wherein thesubstrate is at least partly transmissive to the laser beam and thesemiconductor layer is irradiated through the substrate.
 11. The methodas claimed in claim 1, wherein, prior to separation from the substrate,the semiconductor layer is applied onto a carrier on a side remote fromthe substrate.
 12. The method as claimed in claim 11, wherein thethermal expansion coefficient of the carrier a_(HL) is chosen in amanner coordinated with at least one of the beam profile and the pulselength of the laser beam pulses and with the thermal expansioncoefficient of the semiconductor layer a_(HL) and the thermal expansioncoefficient a_(HL) of the substrate, in order to reduce strains betweenthe substrate, the semiconductor layer, and the carrier duringproduction.
 13. The method as claimed in claim 12, wherein the thermalexpansion coefficient of the carrier a_(HL) is chosen to be nearer tothe thermal expansion coefficient of the semiconductor layer a_(HL) thanto the thermal expansion coefficient as of the substrate.
 14. The methodas claimed in claim 11, wherein the thermal expansion coefficient of thecarrier a_(HL) differs from the thermal expansion coefficient a_(HL) ofthe substrate by 45% or less.
 15. The method as claimed in claim 11,wherein the thermal expansion coefficient of the carrier differs fromthe thermal expansion coefficient a_(HL) of the semiconductor layer by35% or less.
 16. The method as claimed in claim 11, wherein the carrierhas a thermal expansion coefficient of approximately 4.3*10⁻⁶K⁻¹ andapproximately 5.9*10⁻⁶K⁻¹.
 17. The method as claimed in claim 11,wherein the carrier comprises at least one of gallium arsenide, silicon,copper, iron, nickel, cobalt, molybdenum, tungsten, and germanium. 18.The method as claimed in claim 11, wherein a large pulse length of thelaser beam pulses is chosen for the separation of the semiconductorlayer from the substrate.
 19. The method as claimed in claim 11, whereinthe thermal expansion coefficient of the carrier a_(HL) differs from thethermal expansion coefficient a_(HL) of the semiconductor layer by 35%or more, and in which a small pulse length of the laser beam pulses ischosen for the separation of the semiconductor layer from the substrate.20. The method as claimed in claim 11, wherein the semiconductor layeris soldered onto the carrier by means of a solder comprising at leastone of gold, tin, palladium and indium.
 21. The method as claimed inclaim 1, wherein, before the semiconductor layer is connected to thecarrier, a metallization is applied to the side of the semiconductorlayer which is remote from the substrate.
 22. The method as claimed inclaim 21, wherein the metallization comprises at least one of gold andplatinum.
 23. The method as claimed in claim 1, wherein thesemiconductor layer comprises a plurality of individual layers.
 24. Themethod as claimed in claim 1, wherein the III-V compound semiconductormaterial is a nitride compound semiconductor material.
 25. The method asclaimed in claim 24, wherein the semiconductor layer or at least one ofthe individual layers comprises In_(x)Al_(y)Ga_(1-x-y)N where 0≦x≦1,0≦y≦1 and x+y≦1.
 26. The method as claimed in claim 1, wherein thesubstrate comprises at least one of silicon, silicon carbide, aluminiumoxide, sapphire.
 27. The method as claimed in claim 1, wherein thesemiconductor layer is epitaxially grown on the substrate.
 28. Themethod as claimed in claim 1, wherein the semiconductor layer has athickness which is less than or equal to 50 μm.
 29. The method asclaimed in claim 1, wherein the semiconductor component is a lightemitting diode.
 30. The method as claimed in claim 1, wherein aninterface region between semiconductor layer and substrate is irradiatedin such a way that the radiation energy is absorbed at said interfaceregion, said absorption of radiation energy leading to a materialdecomposition within the semiconductor layer.
 31. The method as claimedin claim 3, wherein the noble gas-halogen compound is XeF, XeBr, XeCl,KrCl, or KrF.
 32. The method as claimed in claim 1, wherein the laserbeam is focused onto the semiconductor layer in such a way that, withinthe irradiated region, the energy density generated by the laser beam isbetween 150 mJ/cm² and 800 mJ/cm².
 33. The method as claimed in claim11, wherein the thermal expansion coefficient of the carrier a_(HL)differs from the thermal expansion coefficient a_(HL) of the substrateby 40% or less.
 34. The method as claimed in claim 11, wherein thethermal expansion coefficient of the carrier a_(HL) differs from thethermal expansion coefficient a_(HL) of the semiconductor layer by 25%or less.
 35. The method as claimed in claim 11, wherein the carrier hasa thermal expansion coefficient of approximately 4.6×10⁻⁶K⁻¹ andapproximately 5.3*10⁻⁶K⁻¹.
 36. The method as claimed in claim 25,wherein the semiconductor layer or at least one of the individual layerscomprises GaN, A1GaN, InGaN, AlInGaN, AlN or InN.
 37. The method asclaimed in claim 11, wherein, prior to separation from the substrate,the semiconductor layer is soldered onto a carrier on a side remote fromthe substrate.
 38. The method as claimed in claim 11, wherein a pulselength of greater than 15 ns of the laser beam pulses is chosen for theseparation of the semiconductor layer from the substrate.
 39. The methodas claimed in claim 11, wherein the thermal expansion coefficient of thecarrier a_(HL) differs from the thermal expansion coefficient a_(HL) ofthe semiconductor layer by 35% or more, and in which a pulse length ofless than approximately 15 ns of the laser beam pulses is chosen for theseparation of the semiconductor layer from the substrate.